Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 312337 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 737 PM EDT TUE MAY 31 2016 .SYNOPSIS... A cold front crossing Southern New England moves offshore tonight. High pressure builds over New England with dry and cooler weather Wednesday and Thursday. Two weather systems may bring unsettled weather, one Friday night and the second on Sunday and Monday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 7PM Update... SKC across much of the region this evening after most stratus has burned off the Cape/Islands. Front remains stalled and has actually even retrograded just slightly. Currently it stretches from IJD-PVD-GHG. Not much current forcing to push this front further S, but it should make gradual progression and washout during the overnight hours. Areas S of this front at risk for another round of fog which could be locally dense thanks to dwpts remaining in the 60s. Latest HRRR/RAP do highlight mainly the Cape/Islands for this risk and some still sits off the coast of LI. Tonight... Shortwave moving along the Canadian border drives a second cold front south across New England. Not much moisture aloft with either cold front as they cross our area, so limited clouds at best. Mostly, a wind shift from the north overnight. Temperatures in the upstream airmass started the morning in the upper 40s and 50s. Expect min temps here mainly in the 50s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday... High pressure shifts east over the Maritimes. This will bring mostly sunny skies to Southern New England. This will shift our wind direction to more of a NE or E direction. The flow off the waters to our east will bring cooler temps to the eastern portion of our area. Western areas will modify a little but still remain seasonable. Temps aloft at 850 mb will be 11-12C which would support max sfc temps in the lower 80s. We will forecast that for the CT Valley with temps mostly in the 70s farther east and 60s along the MA east coast. Wednesday night... Maritime High pressure remains in control with mostly clear skies and light east wind. Temperatures may cool a little more than tonight but still mainly in the 50s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... */ HIGHLIGHTS... - A bit of a chill Thursday and Friday with onshore flow - Cold front and wet weather for late Friday into Friday night - Unsettled and prolonged cool, wet weather by early next week Overview and model preferences... A fairly summer-like weak and near zonal flow regime remains in place across the CONUS through much of the long term forecast period. Only a couple of weak and not overly deep shortwaves to contend with. The first arrives Friday but weakens as it meets confluent flow across the NE and inverted ridging at the sfc from high pres in the Maritimes. The second looks to phase with the weak srn stream heat-trof currently over the SW CONUS. This feature does deepen such that H5 heights drop to about 2 std deviations below normal as pointed out by the previous forecaster. Therefore, following the weekend, a slight cooling/unsettled pattern looks to develop, but at this point no major issues are expected as PWATs will remain near normal. An ensemble based blend will be used as a baseline. Details... Thu and Thu night... Inverted ridging out of the Maritimes defines the WX. Plenty of subsidence and dry air supports mainly dry conditions. However, pres gradient continues to support onshore flow which will keep eastern areas of MA/RI likely near or even blow normal in spite of the sunshine as Gulf of Maine SSTs are still (generally as low as 10C offshore). Therefore, expect ranges from the upper 50s right on the water, to 60s inland, and mid-upper 70s in the CT valley and points W of the Worcester Hills. Mins drop into the low 50s thanks to some weak radiational cooling. Fri and Fri night... Weakening shortwave and attendant low pres move ENE through ON and QC, dragging a slowing cold front across the northeast. Low lvl convergence and f-gen apparent, but moisture lacks as it loses it`s connection to the parent low and the tropical moisture within the S stream. Not overly unstable even by afternoon peak heating as lapse rates are modest and below 6C/km, and little sfc based CAPE is forecast. However, do note the risk for a slight increase in shra activity during the afternoon and evening hours thanks to some diabatic support. POPs will reflect this increasing through the day, then diminishing during the overnight hours as the front slowly drifts offshore. In spite of the increased cloud cover, temps actually warmer across the board thanks to return flow and H85 temps increasing to around +14C. Expect highs mainly in the mid-upper 70s with lows only dropping into the 60s. Sat... Although the front shifts offshore, upper lvl weak shortwave yields cyclonic curvature and H5 temps drop to nearly -14C. While this will certainly promote increased afternoon cloud cover, it could also support some afternoon pop shra or maybe even an isolated T-storm. Forcing is weak and destabilization is modest, so not expecting anything widespread. H85 temps averaging +12C would still support highs increasing into the low-mid 70s especially before increasing clouds. Sun and Mon... Warm front approaches Sun and attempts to cross in advance of deepening cutoff and attendant low pres moving into the great lakes. Increasing moisture expected to yield PWATs about 1-std deviation above normal. Good setup for overruning and potential embedded convection as the upper levels cool. Periods of rain and potential for embedded t-storms at times. Temps near to slightly above normal dependent on how deep into the warm sector srn New England can get before low pres moves in from the Great Lakes. Tue and Wed... Unsettled and potentially cooler as low pres and upper lvl cutoff may stack and setup over srn New England. Diurnally driven rainfall possible, along with cooler temps as H85 temps could fall as low as +6C. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/... Through tonight...moderate confidence. VFR most locations, however risk of dense fog with localized IFR/LIFR conditions mainly ACK/HYA/FMH/MVY. Confidence on timing both in and out is low. Otherwise, winds shift from WSW to mainly E by morning. Tomorrow...High confidence. Mainly VFR after any fog dissipates. Winds mainly E. Tomorrow night...Moderate confidence. At issue is the development of more fog and low stratus this time potentially impacting the E coast terminals. For now, expect mainly VFR through much of the night but with a risk for developing lower categories toward morning. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Thursday through Sunday/... Thursday into Friday...High confidence. VFR. E onshore flow, breezy especially across E-coastal terminals, turning SE late. Late Friday into Friday Night...Moderate Confidence. MVFR / Low-End VFR. S flow, potentially breezy, backing W/NW. SHRA possible. Saturday into Sunday...Moderate Confidence. VFR. Breezy N/NE flow persists becoming light towards Sunday morning. Rain possible with localized IFR/MVFR conditions later in the day on Sunday. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. Tonight... Fog redevelops around parts of Cape Cod and Islands bringing poor vsbys. Fog should dissipate toward morning. Winds 20 knots or less from the Southwest will shift from the North overnight. A South swell will remain at 4 feet or less. Wednesday... Winds shift from the Northeast and East but remain below 20 knots. Seas remain less than 5 feet as the South swell slowly diminishes. Wednesday night... East winds 15 knots or less. Seas mostly 3 feet or less but some 4 foot seas possible on the outer waters. Outlook /Thursday through Sunday/... Thursday into Friday...High Confidence. Easterly onshore flow turns to the south on Friday, but generally remains below 20 kt through the period. Seas mainly 4 ft or less. Some shra possible Fri. Saturday into Sunday...Moderate Confidence. N/NE flow persists becoming light towards Sunday morning as high pressure moves across the region. Waves remaining below 5-feet. Some rain possible Sunday afternoon and overnight. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/Doody NEAR TERM...WTB/Doody SHORT TERM...WTB LONG TERM...Doody AVIATION...WTB/Doody MARINE...WTB/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.